Aluminum alloys with copper, e.g. the Series 1000, 2000 and 7000 aluminum alloys, are extensively used in architectural, aircraft and marine applications, and as such are desirably improved in corrosion resistance without adverse trade-offs such as increased weight or discoloration. At the same time, increasing environmental concerns dictate that improvements be obtained without undue use of environmentally hazardous chemicals in anodizing, such as chromates.
In U.S. Pat. No. 5,169,548 to Shulman and Bauman, improvements in corrosion resistance of aluminum were obtained by conditioning a freshly anodized aluminum surface with alcohol and treating with a fatty acid. Corrosion resistance to as much as 2856 hours was obtained using stearic acid and isopropyl alcohol. This technique avoided the problems inherent in use of highly heated baths of fatty acid for this purpose as previously taught, e.g. in U.S. Pat. No. 4,130,466 to Kramer.
Industrial scale application of fatty acid sealing with the use of an alcohol solvent raises concerns of fire hazard, when conducted indoors, and there is need to obtain the benefits of fatty acid sealing of aluminum surfaces without the flammability difficulties accompanying use of an organic solvent for the fatty acid.